摘要:

Two-dimensional Raman scattering is presented as a technique for the monitoring of electric field-induced, submolecular reorientation in liquid crystals. The motions of the flexible part and the rigid core of 4-pentyl-(4-cyanophenyl)cyclohexane (PCH5) are independently monitored in response to both step and oscillatory electric fields. Step voltage experiments show that the flexible group reorients before the rigid core. Also, oscillatory electric field experiments demonstrate that the flexible and rigid groups reorient asynchronously. In fact, at periodicities that are shorter than the bulk reorientation times, it is observed that the reorientation of the flexible part is amplified, while the motion of the rigid core is inhibited. The data suggest that the flexible group possesses a small, local dielectric anisotropy that can couple with the electric field to induce an independent, cooperative reorientation when the mobility of the rigid core is restricted.

ISSN:0267-8292    

DOI:10.1080/026782998205769

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new kind of aligning material for liquid crystal cells, ladder-like polysilsesquioxanes (LPS) grafted with cinnamoyl side groups, has been developed to improve the thermal stability of the photoalignment layer. The LC aligning ability of the LPS-based alignment layers, fabricated by linearly polarized UV-induced polymerization (LPP), was characterized by polarizing optical microscopy, conoscopic observations and electro-optic response measurements. In particular, a practical and severe annealing test was adopted to examine the thermal stability of the alignment layer; this showed that even when LC cells were annealed at 100 C (much higher than the clearing point of the LC) for several hours, good LC orientation could remain when the cell was cooled to a constant measurement temperature. The results confirmed that the photoalignment layers exhibited not only good LC aligning ability, but also excellent thermal stability, so heralding their potential application in LCDs.

ISSN:0267-8292    

DOI:10.1080/026782998205778

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A novel family of bis[(4-alkoxyphenyl)ethynyl]mercury liquid crystals has been synthesized. Their mesomorphism has been studied by DSC and polarizing microscopy and a very broad SmA phase has been found.

ISSN:0267-8292    

DOI:10.1080/026782998205787

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Two kinds of acrylate monomers, i.e. 4-methoxyphenyl 4-{[2-(1-oxo-2-propenyloxy)ethyl]oxy}benzoate (I) and 4-methoxyphenyl 4-{[6-(1-oxo-2-propenyloxy)hexyl]oxy}benzoate (II) were polymerized using hyperbranched poly(p-chloromethylstyrene) (PCMS) as an initiator by atom transfer radical polymerization (ATRP). The resulting dendritic graft copolymers were characterized by means of gel permeation chromatography, differential scanning calorimetry, and polarization microscopy. The mesophase behaviour of these dendritic copolymers essentially depends on the chemical nature of the polyacrylates.

ISSN:0267-8292    

DOI:10.1080/026782998205796

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor